Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Honolulu HI
355 PM HST Fri Oct 21 2016
strong trade winds will persist through the weekend and will
supply periods of wet weather to the area. Trades will focus most
of the shower activity across windward and Mauka areas, but many
of the showers will carry over to leeward sides of the smaller
islands at times. A drier airmass will move into the region next
week, bringing more typical trade wind weather back into the area.
Showers from an old front may move across the islands Wednesday
a 1029 mb surface high is located 850 miles north of Kauai, and
is driving the strong trade winds across the island chain. The
high is slowly weakening, but building closer to Hawaii which is
essentially maintaining a tight pressure gradient and winds over
the state. A Wind Advisory is in effect for portions of The Big
Island and Maui County through 9 PM HST this evening, but windy
and blustery conditions will continue this weekend.
Visible satellite imagery shows mostly cloudy skies windward and partly
cloudy skies leeward across most of the state. Radar shows numerous
showers moving into windward areas carried by the trade winds,
with many the showers reaching leeward areas. Most of the showers
have been concentrated over the smaller islands today, which should
be trend into tonight. Showers are expected to expand southward
towards The Big Island later tonight. Shower coverage may begin to
decrease across the western end of the state by Saturday afternoon,
but not go away completely.
The high 850 miles to the north will dig closer to Hawaii over
the next day allowing the trade winds to strengthen slightly above
the current level. Winds are expected to peak on Saturday and
Saturday night, before trending down on Sunday through Tuesday. A
Wind Advisory has been issued for most of the state for Saturday
into Saturday evening. Strong sustained winds can be expected in
exposed areas to the trade winds and through gaps in the mountains.
Downsloping gusts will be possible for leeward areas. Please see
the Wind Advisory product (npwhfo) on our website for more
The high will weaken north of the state Monday into Tuesday,
allowing the trade winds to ease to moderate to locally fresh
levels. A more typical trade wind weather regime is expected
Monday and Tuesday, with a slight increase in showers possible on
Wednesday evening as a weak frontal boundary pushes through the
island chain. The trades will then strengthen by late next week
as another strong high builds well north of the Aloha state.
radar VAD wind profiles and amdar soundings from Honolulu/Lihue/
Kahului show 30 knots of wind within a few thousand feet of the
surface. Inversions remain weak and elevated, but winds this
strong should still support turbulence in the Lee of the
mountains and an airmet is in effect for moderate low-level
turbulence. The turbulence threat will increase tonight as the
inversion lowers and low-level winds remain just as strong.
Moderate turbulence potential will continue through the weekend,
and possibly into early next week.
A pocket of moisture extends from Kauai to Maui. This airmass is
quite showery, with brief IFR visibilities in the heavier showers.
MVFR conditions will be more widespread across windward sections,
and an airmet is in effect for mountain obscuration. With the
strong trade winds and elevated inversion, occasional showers will
spread leeward and brief MVFR conditions are also possible.
Conditions will begin to improve this evening as a more stable
airmass builds across the state.
a Small Craft Advisory (sca) covers all coastal waters tonight,
and will continue for most areas through the weekend due to
strong trade winds. Winds are forecast to reach gale strength in
the typically windy areas around The Big Island and Maui Saturday
and Saturday night. A Gale Warning GOES into effect these typical
windy areas for Saturday and Saturday night. Please see list of
affected areas below and the marine weather message (mwwhfo)
product on our website. The trades will gradually weaken Sunday
through Tuesday with the areas under the Small Craft Advisory likely being scaled
back to the typically windy waters early next week.
The strong trades, along with the upstream fetch, will build surf
for east facing shores beginning tonight and Saturday, possibly reaching
advisory levels by Saturday night and Sunday. Elsewhere, there
will be a series of small north to northwest swells this weekend
and Monday, with a moderate west northwest swell expected Tuesday.
Small swells will persist for south facing shores into next week.
Wind Advisory until 9 PM HST this evening for Lanai-Kahoolawe-
Maui leeward west-Maui Central Valley-south Big Island-Big
Island north and east-kohala.
Wind Advisory from 6 am to 9 PM HST Saturday for all of Hawaii
except for Kona, Big Island summits and Haleakala Summit.
Small Craft Advisory until 6 am HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island leeward waters-Big
Island southeast waters.
Gale Warning from 6 am Saturday to 6 am HST Sunday for Maalaea
Bay-Pailolo Channel-Alenuihaha Channel-Big Island leeward waters-
Big Island southeast waters.
Small Craft Advisory until 6 am HST Monday for rest of Hawaiian